Spitale, J., Porco, C. and Colwell, J (2006). "Shapes and Kinematics of Eccentric Features in Saturn's Rings from Cassini Imaging and Occultation Observations." American Astronomical Society, DPS meeting #38, #51.05.
Using high-resolution time-lapse sequences and azimuthal imaging scans, together with Cassini and historical occultation observations, we have examined the shapes and kinematics of the major eccentric features in Saturn's rings: The outer edges of the A and B rings, and the narrow ringlets at 1.29, 1.45, 1.47, 1.495, and 1.95 Rs.|
The B-ring outer edge shows the expected two-lobed shape rotating with the mean motion of Mimas, but with periapse leading the satellite by about 28 deg. That m=2 solution yields high residuals, which might be largely explained by a three-lobed pattern rotating at about 505.5 deg/day. In addition to its dominant m=1 freely-precessing elliptical mode, the Huygens ringlet also shows an m=2 shape with a pattern speed equal to, and phase almost exactly opposite to, that of the B-ring outer edge. That precise anti-alignment may indicate that the phase of the Huygens ringlet is controlled by both the Mimas 2:1 resonance and the B-ring outer edge, though the effect of the large-amplitude Mimas libration may also be present. The narrow ringlet 100 km exterior to the Huygens ringlet exhibits unusual behavior, a preliminary analysis suggests that it may have a multi-km vertical excursion. The outer edge of the A ring shows six broad lobes, consistent with previous Voyager-era conclusions that it is distorted by the 7:6 Lindblad resonance with the co-orbital satellites, but the shape deviates strongly from a pure sinusoidal pattern.
Where high azimuthal resolution is available, the above ring edges typically show complicated structure superimposed on the reported Fourier modes. Some of that structure is easily attributed to transient effects from nearby satellites, but much of it is as yet unexplained.